Ip mobility in a communication system

ABSTRACT

A method for routing data packets to a mobile node in a communication system which includes at least a first subnetwork of a first type supporting a first IP version and a second subnetwork of a second type supporting a second IP version. The mobile node is provided with a set of protocol stacks for handling data packets at least according to the first and the second IP version and with a home address at least according to the first and the second IP version. The home agent is provided with means for intercepting at least data packets addressed to the mobile node&#39;s home address according to the first or the second IP version and for encapsulating a data packet addressed to the mobile node in a packet according to the IP version of the foreign network to which said mobile node is attached, for routing the data packet to the mobile node.

FIELD OF THE INVENTION

[0001] The invention relates to mobility support of Internet-typeprotocol traffic in a communication system.

BACKGROUND OF THE INVENTION

[0002] Originally, Internet Protocol (IP) providing access to theInternet was designed for stationary users. Therefore, the basic IPconcept does not support user mobility: The IP addresses are assigned tonetwork interfaces depending on their location in the network. In fact,the first part of an IP address (NETID) is common to all interfaces thatare linked to the same Internet subnetwork. This scheme prevents a user(a mobile host) from being reachable while moving over differentInternet subnetworks, i.e. while changing the physical interface.

[0003] In order to enhance mobility on the Internet, Mobile IPs for IPversion 4 (MIPv4) and IP version 6 (MIPv6) have been introduced by theInternet Engineering Task Force (IETF) in the standard RFC2002 and inthe Internet Draft “Mobility Support in IPv6”, Jun. 25, 1999 (work inprogress), respectively. A Mobile IP enables a mobile host to change itspoint of attachment from one Internet subnetwork to another withoutchanging its IP address. The mobile IP introduces the following newfunctional or architectural entities. For the sake of brevity, the term‘IP’ will hereafter refer to Mobile IP.

[0004] A ‘Mobile Node’ (MN) refers to a host that changes its point ofattachment from one network or subnetwork to another. A mobile node maychange its location without changing its IP address; it may continue tocommunicate with other Internet nodes at any location using its(constant) IP address.

[0005] A ‘Correspondent Node’ (CN) refers to a peer node with which amobile node is communicating. The correspondent node may be eithermobile or stationary.

[0006] A ‘Home Network’ is the IP network to which a user logicallybelongs. Physically, it can be, for example, a local area network (LAN)connected via a router to the Internet. A ‘Home Address’ is an addressthat is assigned to a mobile node for an extended period of time. It mayremain unchanged regardless of where the MN is attached to the Internet.Alternatively, it could be assigned from a pool of addresses.

[0007] A ‘Home Agent’ (HA) is a routing entity that intercepts anypackets destined to the mobile node's home address, while the mobilenode is away from the home network. The HA encapsulates packets fordelivering them to the mobile node, and maintains current locationinformation for the mobile node.

[0008] In Mobile IPv4, a ‘Foreign Agent’ (FA) is a routing entity in amobile node's visited network, which provides routing services to themobile node while it is registered in that particular network, thusallowing the mobile node to utilize its home network address. Theforeign agent decapsulates the packets that were encapsulated by themobile node's home agent and delivers them to the mobile node. Fordatagrams sent by a mobile node, the foreign agent may serve as adefault router.

[0009] RFC2002 defines a ‘Care-of Address’ (COA) for Mobile IPv4 as thetermination point of a tunnel towards a mobile node for datagramsforwarded to the mobile node while it is away from home. The protocolcan use two different types of care-of addresses: a “foreign agentcare-of address” is an address announced by a foreign agent with whichthe mobile node is registered, and a “co-located care-of address” is anexternally obtained local address which the mobile node has acquired inthe network. An MN may have several COAs at the same time. A COA of a MNis registered with its HA. The list of COAs is updated when the mobilenode receives advertisements from foreign agents. If an advertisementexpires, its entry or entries should be deleted from the list. Oneforeign agent can provide more than one COA in its advertisements.

[0010] In Mobile IPv6, there is no longer a need to deploy specialrouters as FAs. Mobile nodes make use of the enhanced features of IPv6to operate in any location away from home without requiring any specialsupport from their local routers. Most packets sent to a mobile nodeaway from home in Mobile IPv6 are routed using an ‘IPv6 Routing’ headerrather than IP encapsulation, whereas Mobile IPv4 must use encapsulationfor all packets. The use of a Routing header requires less overhead forMobile IP packet delivery from a CN to an MN. To avoid modifying thepacket in flight, however, packets intercepted and routed via a mobilenode's home agent in Mobile IPv6 must still use encapsulation fordelivery. The COA in Mobile IPv6 is the IP address associated with amobile node while it is visiting a foreign network.

[0011] Both in Mobile IPv4 and in Mobile IPv6, the term ‘MobilityBinding’ is the association of a home address with a care-of address,along with the remaining lifetime of that association. An MN registersits COA with its HA by sending a registration request message. In IPv4,the ‘IPv4 Registration Request’ message may be relayed to the HA by theforeign agent through which the mobile node is registering, or it may besent directly to the HA if the mobile node is registering a co-locatedcare-of address. The HA returns an ‘IPv4 Registration Reply’ message tothe mobile node which has sent an IPv4 Registration Request message. Ifthe mobile node has registered by using a foreign agent care-of address,the IPv4 Registration Reply is delivered to the mobile node via theforeign agent. The IPv4 Reply message informs the mobile node about thestatus of its IPv4 Request. Optional extension fields containingadditional information concerning the connection may be included in theIPv4 Registration Request and Reply messages. In IPv6, a mobile nodesends a registration request message directly to the HA, and in responseto the request message, the HA returns a registration reply message tothe mobile node. The registration request and reply messages areincluded in a ‘Destination Options’ header, which is used to carryoptional information that needs to be examined only by the destinationnode. The messages are called ‘Binding Update’ and ‘BindingAcknowledge’, respectively.

[0012] In order to enable full IPv6 functionality of isolated IPv6 nodesin an IPv4 environment, a ‘6over4’ transmission method has beenintroduced in IETF standard RFC2529. The principle is that IPv6 packetsare encapsulated in IPv4 packets for transmission over the IPv4 networkbetween isolated IPv6 nodes.

[0013] A real advantage of IPv6 over IPv4 is that the former containsrouting optimization by default, i.e. the home agent is involved onlywhen the first datagram is sent to the mobile node on the connectioninitiation, hence reducing the overhead required. However, an IPv6network is not available everywhere and not all user terminals areequipped with IPv6 compatibility. Since the addressing schemes in thetwo versions are incompatible, the IPv4 and IPv6 nodes cannotcommunicate with each other in a straight-forward manner.

DISCLOSURE OF THE INVENTION

[0014] An object of the invention is to develop a method and acommunication system which provide mobile nodes with means forcommunicating over networks supporting different IP versions and withmeans for being simultaneously addressable with IP addresses accordingto at least two different IP versions irrespective of the type of theparticular network that the mobile node is attached to.

[0015] This object is achieved with a method and a system which arecharacterized by what is disclosed in the attached independent claims.Preferred embodiments of the invention are disclosed in the attacheddependent claims.

[0016] According to a preferred embodiment of the present invention, amobile node is arranged to handle data packets at least according to twodifferent IP versions and to have a home address at least according tosaid two IP versions. The home agent is provided with means forintercepting all data packets destined to the mobile node irrespectiveof the original IP version of the data packets. In the home agent, adata packet addressed to the mobile node is encapsulated in a packetaccording to the IP version of the foreign network with which the mobilenode is registered, for routing the data packet to the mobile node. Thismethod improves the employment of the network resources.

[0017] According to a further preferred embodiment of the presentinvention, a mobile node is registered with at least a first and asecond foreign network so that the respective first and second care-ofaddresses are simultaneously active in the home agent of the mobilenode, and data packets according to at least the first and the second IPversion are routed to the mobile node (MN) via the home agent by usingthe IP version of the first and the second foreign network respectively.This embodiment can be implemented by means of a new extension field inthe registration request message. The advantage of this method issmaller overhead in the visited network.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the following, the invention will be described in greaterdetail by means of preferred embodiments with reference to theaccompanying drawings, in which

[0019]FIGS. 1A and 1B illustrate scenarios where a mobile node in anIPvY foreign network communicates with a correspondent node in an IPvZsubnetwork, Y and Z being different version numbers,

[0020]FIGS. 2A and 2B illustrate scenarios where a mobile node isregistered with an IPv4 foreign network,

[0021]FIG. 3 illustrates a scenario where a mobile node is registeredwith an IPv6 foreign network,

[0022]FIG. 4 is a signaling diagram illustrating data transfer betweenan MN in an IPv4 foreign network and a CN in an IPv6 subnetwork,

[0023]FIG. 5 is a signaling diagram illustrating data transfer betweenan MN in an IPv6 foreign network and a CN in an IPv4 subnetwork,

[0024]FIGS. 6A and 6B illustrate scenarios where a mobile node registerswith both IPv4 and IPv6 foreign networks,

[0025]FIG. 7 is a signaling diagram illustrating the registration of theMN when the MN first registers with an IPv6 foreign network,

[0026]FIG. 8 is a signaling diagram illustrating the registration of theMN when the MN first registers with an IPv4 foreign network,

[0027]FIG. 9 is a signaling diagram illustrating data transfer when theMN is registered with both IPv4 and IPv6 foreign networks, and

[0028]FIG. 10 illustrates a registration request message according tothe invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention can be generally applied to a network thatincludes at least two subnetworks supporting different IP versions forproviding IP mobility over the subnetworks. The invention can be usedespecially preferably for providing IP mobility over IPv4 and IPv6subnetworks. In the following, preferred embodiments of the inventionwill be described by means of said IP versions without limiting theinvention to these particular IP versions.

[0030] The network may be, for example, a local area network (LAN) orany other kind of network providing data connections. The network may beeither wireless or fixed. The greatest advantages are achieved in anetwork providing a relatively slow data connection. The MN may consistof a laptop computer PC connected to a mobile station radio or someother type of mobile workstation construction. Alternatively, the MN canbe an integrated combination of a small computer and a cellulartelephone, similar in appearance to the Nokia Communicator 9000 series.Yet further embodiments of the MN are various pagers, remote-control,surveillance and/or data-acquisition devices, etc.

[0031]FIGS. 1A and 1B illustrate simplified scenarios where a mobilenode MN is attached to a foreign network 16 supporting IP version Y. Acorrespondent node CN is attached to a subnetwork 14 supporting IPversion Z and another correspondent node CN′ is attached to a subnetwork18 supporting IP version Y. The mobile node MN is provided with a homeaddress according to IP versions Y and Z and with means to handle datapackets according to both versions. A home agent HA in said mobilenode's MN home network 12 intercepts all packets destined to the mobilenode MN regardless of their type and the type of the foreign networkwith which the mobile node MN is registered.

[0032] In FIG. 1A, the home agent HA encapsulates an IPvY data packetdestined to the mobile node's IPvY home address normally in an IPvY datapacket IPvY[IPvY] and an IPvZ data packet destined to the mobile node'sIPvZ home address in an IPvY data packet IPvY[IPvZ] for delivery to themobile node MN. The data packets IPvY[IPvY] and IPvY[IPvZ] are routeddirectly to the mobile node MN. In FIG. 1B, the mobile node MN isregistered with the IPvY foreign network via a foreign agent FA and thedata packets are routed to the mobile node MN via the foreign agent FA.The home agent HA encapsulates an IPvY data packet destined to themobile node's IPvY home address normally in an IPvY data packetIPvY[IPvY] for delivery to the mobile node MN via the foreign agent FA.The home agent HA also encapsulates an IPvZ data packet destined to themobile node's IPvZ home address in an IPvY packet for the mobile node MNand further in another IPvY packet for the foreign agent FA, resultingin a multiply-encapsulated data packet IPvY[IPvY[IPvZ]]. Therefore, bothin FIG. 1A and in FIG. 1B, the correspondent node CN may send datapackets according to IP version Z to the mobile node MN without anyaddress transformation, even though the mobile node MN is not attachedto a network supporting IP version Z.

[0033]FIGS. 2A, 2B and 3 illustrate simplified scenarios where a mobilenode MN and a correspondent node communicate over IPv4 and IPv6subnetworks. The mobile node MN is provided with means to operate bothin IPv4 and IPv6 networks, i.e. to have an IP address according to bothprotocol versions. In other words, the mobile node MN is alwaysaddressable from an external network by both the IPv4 and the IPv6address. The mobile node's home agent HA in a home network 22 isarranged to intercept IPv4 and IPv6 packets destined to the mobile nodeMN regardless of their type. In FIGS. 2A and 2B, the mobile node MN isattached to an IPv4 foreign network 26 and a correspondent node CNv6 isattached to an IPv6 subnetwork 24.

[0034] In FIG. 2A, the mobile node MN is registered with the IPv4foreign network 26 via a foreign agent FA. The home agent HAencapsulates an incoming IPv6 data packet in an IPv4 packet for themobile node MN and the latter in another IPv4 packet for the foreignagent FA, resulting in a multiply-encapsulated data packetIPv4[IPv4[IPv6]]. In FIG. 2B, the mobile node MN is registered with theIPv4 foreign network without a foreign agent FA. The home agent HAencapsulates an incoming IPv6 data packet in an lPv4 packet for themobile node MN, resulting in a data packet IPv4[IPv6].

[0035] In FIG. 3, the mobile node MN is attached to an IPv6 foreignnetwork 36 and a correspondent node CNv4 is attached to an IPv4subnetwork 34. The home agent HA encapsulates an incoming IPv4 datapacket in an IPv6 packet for the mobile node MN, resulting in a datapacket IPv6[IPv4].

[0036]FIG. 4 is a signaling diagram illustrating data transfer in ascenario according to FIG. 2A. Prior to the data transfer, the mobilenode MN registers normally with the IPv4 foreign network. All IPv4 datapackets destined to the mobile node MN are routed normally according tothe Mobile IPv4 and therefore are not considered here. In step 4-1, thecorrespondent node CNv6 sends an IPv6 data packet to the mobile node'sMN IPv6 address. The home agent HA intercepts the packet andencapsulates it in an IPv4 packet for the mobile node MN and the latterin another IPv4 packet for the foreign agent FA, resulting in amultiply-encapsulated packet IPv4[IPv4[IPv6]] in step 4-2. The foreignagent FA then decapsulates the outer IPv4 packet and forwards theremaining data packet IPv4[IPv6] to the mobile node MN in step 4-3. Inthe mobile node MN, the remaining IPv4 packet is decapsulated by an IPv4stack and the original IPv6 packet is forwarded to an IPv6 stack fornormal processing in step 4-4. In the other direction, the IPv6 stack inthe mobile node MN produces an IPv6 datagram and forwards it to the IPv4stack in step 4-5. In step 4-6, the IPv4 stack encapsulates the originalIPv6 packet into an IPv4 packet and sends the resulting packetIPv4[IPv6] for example to the home agent HA that decapsulates the IPv4packet and forwards the original IPv6 packet to the correspondent nodeCNv6 in step 4-7.

[0037]FIG. 5 is a signaling diagram illustrating data transfer in ascenario according to FIG. 3. Now the mobile node MN registers with theIPv6 foreign network in a normal way, and all IPv6 data packets destinedto the mobile node's MN IPv6 home address are routed normally. In step5-1, the correspondent node CNv4 sends a data packet IPv4 to the mobilenode's MN IPv4 address. The home agent HA intercepts the packet andencapsulates it in an IPv6 packet for the mobile node MN, resulting in apacket IPv6[IPv4] n step 5-2. In the mobile node MN, the IPv6 packet isthen decapsulated by an IPv6 stack and the original IPv4 packet isforwarded to an IPv4 stack for normal processing in step 5-3. In theother direction, the IPv4 stack in the mobile node MN produces an IPv4datagram and forwards it to the IPv6 stack in step 5-4. In step 5-5, theIPv6 stack encapsulates the original IPv4 packet into an IPv6 packet andsends the resulting packet IPv6[IPv4] for example to the home agent HAthat decapsulates the IPv6 packet and forwards the original IPv4 packetto the correspondent node CNv4 in step 5-6.

[0038] Instead of routing MN-originated packets via the HA (steps 4-6and 5-5), such packets may be routed via any other router or entity thatis equipped with means to identify, decapsulate and forward a packet.

[0039]FIGS. 6A and 6B illustrate scenarios according to a furtherembodiment of the invention. The mobile node MN is registeredsimultaneously with an IPv4 foreign network 64 and an IPv6 foreignnetwork 66. If both types of foreign networks are available, the mobilenode MN retains its attachment to the foreign network it has alreadyregistered with and registers also with the other one. Similarly to thescenarios in FIGS. 2A, 2B and 3, the home agent HA intercepts allpackets IPv4, IPv6 destined to the mobile node MN regardless of theirtype. In FIG. 6A, the mobile node MN is registered with the IPv4 foreignnetwork via a foreign agent FA. The home agent HA encapsulates an IPv4datagram in an IPv4 packet IPv4[IPv4] for the foreign agent FA, whichforwards the original IPv4 packet to the mobile node MN.Correspondingly, the home agent HA encapsulates an IPv6 datagram in anIPv6 packet IPv6[IPv6] for the mobile node MN. In FIG. 6B, the mobilenode MN is registered with the IPv4 foreign network without a foreignagent FA. Now the home agent HA encapsulates an IPv4 datagram in an IPv4packet IPv4[IPv4] directly for the mobile node MN. Similarly to FIG. 6A,the home agent HA encapsulates an IPv6 datagram in an IPv6 packetIPv6[IPv6] for the mobile node MN. In this way, unnecessaryencapsulations are eliminated and overhead for the foreign networks isreduced.

[0040]FIG. 7 is a signaling diagram illustrating the registration of themobile node MN in a scenario according to FIG. 6A when the mobile nodeMN first registers with the IPv6 foreign network. Steps 7-1 and 7-2illustrate normal registration with the IPv6 foreign network. Steps 7-3to 7-6 illustrate registration with the IPv4 foreign network via aforeign agent with a ‘Simultaneous IPv6 Binding’ extension. Theextension is similar to for example the ‘Encapsulating Delivery Style’extension header and includes the IPv6 care-of address that will be usedsimultaneously with the IPv4 care-of address.

[0041]FIG. 8 is a signaling diagram illustrating the registration of themobile node MN in a scenario according to FIG. 6A when the mobile nodeMN first registers with the IPv4 foreign work. Steps 8-1 to 8-4illustrate normal registration with the IPv4 foreign network via aforeign agent. Steps 8-5 and 8-6 illustrate the registration with theIPv6 foreign network with a ‘Simultaneous IPv4 Bindings DestinationOption’ extension including the IPv4 care-of address that will be usedsimultaneously with the IPv6 care-of address.

[0042] In FIG. 9, data transfer in a scenario according to FIG. 6A isillustrated in the form of a signaling diagram. The correspondent nodeCNv6 sees the mobile node MN as an IPv6 node and the correspondent nodeCNv4 sees the mobile node MN as an IPv4 node. Steps 9-1 to 9-5illustrate traffic between the correspondent node CNv6 and the mobilenode MN and steps 9-6 to 9-9 illustrate traffic between thecorrespondent node CNv4 and the mobile node MN.

[0043]FIG. 10 illustrates a registration request message 101 accordingto the present invention used for simultaneous registration with an IPv4and an IPv6 foreign network. The first part 102 of the message 101 is anormal registration request. In Mobile IPv4, the part 102 is called anIPv4 Registration Request message, and in Mobile IPv6 said part 102 iscalled a Binding Update and is included in a Destination Options header.The second part 103 of the message 101 is an extension including thecare-of address which is to be used simultaneously with the care-ofaddress according to the first part 102 of the message 101.

[0044] This description only illustrates the preferred embodiments ofthe invention. The invention is not, however, limited to these examples,but it may vary within the scope and spirit of the appended claims.

1. A method for routing data packets to a mobile node (MN) in a communication system which includes at least a first subnetwork of a first type supporting a first IP version and a second subnetwork of a second type supporting a second IP version, the method comprising the steps of attaching the mobile node (MN) to a foreign network of the first type (16, 26, 36, 64, 66); registering the mobile node's (MN) care-of address in the foreign network (16, 26, 36, 64, 66) with a home agent (HA) located in said mobile node's home network (12, 22); characterized by providing the mobile node (MN) with a set of protocol stacks for handling data packets at least according to the first and the second IP version; providing the mobile node (MN) with a home address at least according to the first and the second IP version; providing the home agent (HA) with means for intercepting at least data packets addressed to the mobile node's home address according to the first or the second IP version; and encapsulating in the home agent (HA) a data packet addressed to the mobile node (MN) in a packet according to the IP version of the foreign network (16, 26, 36, 64, 66) to which said mobile node (MN) is attached, for routing the data packet to the mobile node (MN).
 2. A method according to claim 1, characterized by attaching the mobile node (MN) at least to a foreign network of the second type (66, 64); registering at least the mobile node's (MN) care-of address in the foreign network of the second type (66, 64) with the home agent (HA), so that the care-of addresses at least in the foreign networks of the first and the second type are simultaneously active in the home agent (HA) of said mobile node (MN); and encapsulating in the home agent (HA) at least a data packet addressed to the mobile node's home address according to the first IP version in a data packet according to the first IP version, and a data packet addressed to the mobile node's home address according to the second IP version in a data packet according to the second IP version, for routing the data packets to the mobile node (MN).
 3. A method according to claim 2, characterized in that registering the mobile node (MN) with the foreign network of the second type (66, 64) is accomplished by using a registration request message (101) which includes an extension containing at least the care-of address of the mobile node (MN) in said foreign network of the first type (64, 66).
 4. A method according to any one of the preceding claims, characterized in that the first IP version is IPv4 and the second IP version is IPv6.
 5. A method according to any one of claims 1 to 3, characterized in that the first IP version is IPv6 and the second IP version is IPv4.
 6. A communication system for routing data packets to a mobile node (MN), the system comprising at least a first subnetwork of a first type supporting a first IP version and a second subnetwork of a second type supporting a second IP version, wherein the first subnetwork is the mobile node's foreign network (16, 26, 36, 64, 66); a home agent (HA) located in the mobile node's (MN) home network (12, 22), for registering the mobile node's (MN) care-of address in the foreign network (16, 26, 36, 64, 66); characterized in that the system is adapted to provide the mobile node (MN) with a home address at least according to the first and the second IP version; and the home agent (HA) is adapted (a) to intercept at least data packets addressed to the mobile node's (MN) home address according to the first or the second IP version; and (b) to encapsulate a data packet addressed to the mobile node (MN) in a packet according to the IP version of the foreign network (16, 26, 36, 64, 66) to which the mobile node (MN) is attached, for routing the data packet to the mobile node (MN).
 7. A communication system according to claim 6, characterized in that the home agent (HA) is further adapted to accept a registration of at least a second care-of address of the mobile node in a foreign network of the second type (64), so that the care-of addresses at least in the foreign networks of the first and the second type are simultaneously active in the home agent (HA); and to encapsulate at least a data packet addressed to the mobile node's home address according to the first IP version in a data packet according to the first IP version, and a data packet addressed to the mobile node's home address according to the second IP version in a data packet according to the second IP version, for routing the data packets to the mobile node (MN).
 8. A home agent (HA) for routing data packets to a mobile node (MN) in a communication system which includes at least a first subnetwork of a first type supporting a first IP version and at least a second subnetwork of a second type supporting a second IP version, the home agent (HA) being located in the mobile node's (MN) home network (12, 22); and arranged to accept a registration of the mobile node's first care-of address in a foreign network of the first type (16, 26, 36, 64, 66) to which the mobile node (MN) is attached; characterized in that the home agent (HA) is arranged to cooperate with a mobile node (MN) which is provided with (a) a set of protocol stacks for handling data packets at least according to the first and the second IP version, and (b) a home address at least according to the first and the second IP version; is provided with means for intercepting at least data packets addressed to the mobile node's (MN) home address according to the first or the second IP version; and is arranged to encapsulate a data packet addressed to the mobile node (MN) in a packet according to the IP version of the foreign network (16, 26, 36, 64, 66) to which said mobile node (MN) is attached, for routing the data packet to the mobile node (MN).
 9. A home agent (HA) according to claim 8, characterized in that the home agent (HA) is arranged to accept a registration of the mobile node's second care-of address in a foreign network of the second type (66, 64), so that the care-of addresses at least in the foreign networks of the first and the second type are simultaneously active in the home agent (HA); and to encapsulate at least a data packet addressed to the mobile node's home address according to the first IP version in a data packet according to the first IP version, and a data packet addressed to the mobile node's home address according to the second IP version in a data packet according to the second IP version, for routing the data packets to the mobile node (MN).
 10. A mobile node (MN) for a communication system which includes at least a first subnetwork of a first type supporting a first IP version and at least a second subnetwork of a second type supporting a second IP version, the mobile node (MN) being arranged to attach to a foreign network of the first type (16, 26, 36, 64, 66); and to register its care-of address in the foreign network (16, 26, 36, 64, 66) with a home agent (HA) located in said mobile node's (MN) home network (12, 22); characterized in that the mobile node (MN) is provided with a set of protocol stacks for handling data packets at least according to the first and the second IP version; provided with a home address at least according to the first and the second IP version; arranged to attach at least to a foreign network of a second type (66, 64); arranged to register a care-of address in the foreign network of the second type (64) with the home agent (HA), so that the care-of addresses at least in the foreign networks of the first and the second type are simultaneously active in the home agent (HA) of the mobile node; arranged to cooperate with the home agent (HA) which is provided with means for intercepting at least data packets addressed to the mobile node's home address according to the first or the second IP version; and arranged to cooperate with the home agent (HA) which encapsulates at least a data packet addressed to the mobile node's home address according to the first IP version in a data packet according to the first IP version, and a data packet addressed to the mobile node's home address according to the second IP version in a data packet according to the second IP version, for routing the data packets to the mobile node (MN).
 11. A registration request message (101) comprising a first part (102) for registration of a mobile node's (MN) second care-of address in a foreign network of a second type (66, 64); characterized in that the registration request message further comprises a second part (103) including a care-of address of the mobile node in a foreign network of a first type (64, 66) to which the mobile node (MN) has attached prior to attaching to the foreign network of the second type (66, 64). 